1. Technical Field
This invention relates to the technology of treating automotive emissions with catalysts to convert and remove HC, CO, and NO.sub.x content (three-way), and more particularly to the technology for treating high temperature exhaust gases (i.e., 800.degree.-1050.degree. C.) such as may be emitted from truck engines.
2. Discussion of the Prior Art
Lanthanum precious metal oxides, other than La-Pd-oxides, have been experimented with for purposes other than for directly enhancing activity of automotive exhaust catalysts. For example, in U.S. Pat. No. 4,127,510, LaRhO.sub.3 was added as a coating to an automotive exhaust catalyst to prevent Rh enrichment during use under oxidizing conditions and relatively low exhaust gas temperatures. Such coating composition of this reference will not and did not achieve the enhancement in three-way catalytic activity sought by this invention at exhaust temperatures of 900.degree.-1050.degree. C., whether the engine is run at fuel-lean or fuel-rich conditions.
Laboratory creation of binary La-Pd-oxides is known (see Attfield J. P., Acta Crystallography, Vol. B44, p. 563, 1988; and Attfield J. P., Ferey G., Journal Solid State Chem., Vol. 80, p. 286, 1989). But, such chemical preparation did not appreciate the effectiveness of such binary oxides to catalyze the conversion of noxious elements of automotive exhaust gases which are at temperatures considerably different than those encountered in the laboratory.
Elements for the creation of such binary oxides (La-Pd-oxides) have been present in mechanical mixtures of La.sub.2 O.sub.3 and palladium, both used as mixed phases of a coating for an automotive exhaust catalyst. However, such mechanical mixture is not stable at temperatures of 900.degree.-1050.degree. C. and does not lead to formation of binary La-Pd-oxides during automotive catalyst use.